Distichoptilum gracile Verrill, 1882

Risaro, Jessica & Abstract, Daniel Lauretta, 2023, Sea Pens (Cnidaria: Octocorallia: Pennatuloidea) From The Mar Del Plata Submarine Canyon And Outskirts, Zootaxa 5389 (4), pp. 401-433 : 413-414

Distichoptilum gracile Verrill, 1882 “b”

Figures 4 , 5 , 6

Synonyms

Distichoptilum gracile : Verrill, 1882; Distichoptilum verrillii Studer, 1894 ; Juncoptilum alcocki Thomson & Henderson, 1905

STUDIED MATERIAL

MACN-IN-44004, 1 specimen, St. 26 (37º52.30’S, 53º57.43’W), August 2012, 1738 m. MACN-IN-44005, 1 specimen, St. 35 (37º54.04’S, 54º24.09’W), May 2013, 1245 m. MACN-IN-44006, 1 specimen, St. 60 (37º51.70’S, 54º4.58’W), September 2013, 1584 m. MACN-IN-43994, 1 specimen, St. 56 (37º54.84’S, 54º2.47’W), September 2013, 2204 m.

DESCRIPTION

Colonies have color variations, from intense-orange to light yellow when fixed in ethanol. Colonies long, narrow and whip like or spiral like ( Fig. 4 , a), of 85 mm – 590 mm (233.4 mm ± 46 mm, N = 4) in length. Rachis 80 mm – 574 mm (200 mm ± 32.6 mm, N = 4) in length and 0.4 mm – 1.43 mm (1.2 mm ± 0.5 mm, N = 4) in diameter in all its extension. Autozooids in two longitudinal and alternate rows of 20 – 264 (91 ± 18, N = 4) autozooids per colony. Sclerites of the autozooids projects from rachis forming calyces with two teeth in its edge; calyces 1 mm – 2.5 mm (3.1 mm ± 1.4 mm, N = 89, variations from two colonies) in length and autozooids completely retracted when fixed ( Fig. 4 , b), siphonozooids minute, only visible with stereoscopic lens. Peduncle short of 4.54 mm – 16 mm (10.5 mm ± 3.8 mm, N = 4) in length and 0.31 mm – 6.20 mm (2.35 mm ± 0.7 mm, N = 4) in diameter in its widest region. Internal axis presents in all its extension, semi-quadrangular in cross section, of 0.21 mm – 1.01 mm (0.7 mm ± 0.4 mm, N = 4) in diameter ( Fig. 5 ). Coenenchyma slightly wrinkled, red or yellow in color given by its conspicuous needle-shaped sclerites, its length varies between tissues and goes from 102.6 µm to 453 µm in rachis and from 374 µm to 565 µm in autozooids ( Fig. 6 ).

Distribution: Cosmopolitan from 800 m to 4200 m depth approximately (Williams 2011). In the studied region has a bathymetric range between 1245 m and 2204 m depth.

REMARKS: This work represents the first record of the species for the SAO off Argentina.

DISCUSSION

Genus Distichoptilum is a monospecific genus, created by Verrill in 1882 and included in the family Protoptilidae Kölliker, 1872 . At the taxonomic level, this genus was not considered a problem for taxonomists, since D. gracile has morphological characters easily recognizable, such as its whiplike shape, the distribution of its autozooids and the shape of its calyces. Previous records locate this species in the coasts of India (Indian Ocean), where it was found for the first time (Verrill 1882 “b”). Lately it was found in the Pacific Ocean and North Atlantic Ocean ( Thomson & Henderson 1906; Deichmann 1936; Williams 1990). During this work four specimens that fully coincide with the diagnostic characters of D. gracile were found despite some color variations. del Río Iglesias et al. (2012) made the first record of the species for the Argentinian Sea, although they did not specify location or depth. Therefore, its distribution in deep waters of the Argentinian Sea extend from Mar del Plata coasts (Buenos Aires province) to Patagonia.

Figures

FIGURE 4. Distichoptilum gracile. A) General aspect of a complete colony after fixed in ethanol. B) Detail of ventral and dorsal views of the colony. Abbreviations: Aut: withdrawn autozooids; Ct: calyx tooth; Ped: peduncle.

FIGURE 5. SEM micrographs of cross section of the central axis of D. gracile. It shows the same form and diameter through its entire length. A) Proximal, between peduncle and rachis. B) Distal, from the most distal region of the colony.

FIGURE 6. SEM micrographs of the diversity of sclerites of D. gracile. A-C) Sclerites from the autozooids calyces. D-F) Sclerites from the rachis.